This study will investigate the effect of various calcifying fluids on the remineralization of enamel caries and artificial caries-like lesions in vitro. The major part of the experimental work will be carried out on artificial caries-like lesions created in acidified gels. Such lesions are indistinguishable from natural caries when examined histologically by polarized light. After creation of artificial lesions, each tooth is slit into test and control halves so that lesions will have suitable controls. In particular, studies will be conducted on: 1) the effect in vitro of calcifying fluids on natural and artificial lesions where just the enamel surface superficial to the lesion is exposed for experiment. 2) the effect in vitro of whole saliva on natural and artificial lesions. 3) the effect of fluoride ions on the remineralization of enamel lesions in vitro. 4) the effect of remineralization on further lesion formation in vitro. 5) the effect of a synthetic salivary pellicle on the enamel surface with respect to the remineralization of enamel lesions in vitro. 6) the effect of exposure of sound human enamel surfaces, with and without synthetic pellicles, to calcifying fluids in vitro. The susceptibility of test and control surfaces to artificial caries will also be investigated.